* [fuzz] Fix signature of `i64.extend32_s` single-instruction test This single-instruction test incorrectly attempted to convert an `i32` to an `i64`; the correct signature is `i64 -> i64`. See the [WebAssembly specification](https://webassembly.github.io/spec/core/bikeshed/#a7-index-of-instructions). * [fuzz] Fix typo in single-instruction function generator Previously, the `unary!` macro created functions that used two operands instead of the expected one.